The production of logs is known to require the supply of a continuous paper web along a predetermined path. At a point of said path, a discontinuous transverse cut is operated on the web in order to subdivide it into portions or sheets of preset length to be separated by a tear.
The formation of logs implies the use of tubular cardboard spools (commonly referred to as “cores”) on the surface of which a preset amount of glues is distributed to allow the glueing of the first sheet of the log to be formed.
The formation makes also use of winder rollers which drive the core, on which the paper winds up, into rotation.
The process of formation of a log terminates after a preset amount of paper has been wound over the core.
At this point, the formation of the next log is started.
Upon completion of the said formation it is necessary to glue the last sheet of each log on the underlying sheet, to avoid the spontaneous unwinding of the same log. This type of glueing is defined “edge closing”.
To this end, downstream of the unit for the formation of the log a suitable glueing device is provided to which all the formed logs are fed. Each log is to be cut transversally afterwards, to obtain therefrom a plurality of rolls of paper of commercial format.
A rewinding machine for the production of logs is described in details in the patent EP 694020.
The above described technique of forming a log requires therefore an auxiliary device for glueing. This weighs heavily on the running costs and demands more space for the production system.
There are also other considerations to be made on the above technique. One important aspect to be considered relates to the procedure for spreading the glue onto the core, as necessary to fix the first sheet of the log to be formed. On the machines presently known, this procedure is carried out outside the winding region: the glue is distributed onto the cores to be used afterwards for the formation of the log, prior to the same cores entering the region in which they come in contact with the paper web. This operating mode, in the case of a prolonged stop of the machine, may lead to the drying of the glue present onto the cores. It should be understood that such a situation, if not suitably rectified, leads to a faulty process. In fact, on the machines of this type, the operator is bound, under such conditions, to remove manually the core previously glued.
A further consideration, again concerning the glue spread onto the core, refers to the stage in which the size of the log becomes increasingly larger between the winding rollers. The weight of the glue applied onto the core, in the case the latter is distributed longitudinally on a rather thick line, is cause for an “unbalance” of the same core which, when considering the speed involved, may induce strong vibrations on the log in the course of formation. This phenomenon, which can be self-intensifying, may lead to the formation of a log in which the core results out of axis.